I am now 99.9% sure it is Galex urceolata.
Sorry Lin but the leaves of Hydrocotyle umbellata are different.
They are like an umbrella with the leaf stalk in the centre of a round leaf...with the veins radiating from a central position.It gets nipped back to roots by winter frosts, but will remain evergreen in subtropical areas.
While Galex leaves look more heart shaped...veins radiate from the stalk at the one end.
See good clear links below....
1st two are Galex..3rd is Hydrocotyle
http://www.carolinanature.com/...
http://www.carolinanature.com/...
https://wildflowerhunter.files...
